1. Field of the Invention
The present invention generally relates to a display apparatus, and more particularly to an apparatus for controlling the illumination of two dependent visual indicators with a single output pin of an integrated circuit.
2. Description of the Related Art
Most electronic devices today, such as a printer, modem, computer, server, pager, phone, etc., utilize visual indicators, such as a light emitting diode (xe2x80x9cLEDxe2x80x9d), to display various operational conditions of the device to the user. In the same conventional devices, each visual indicator is independently driven using separate pins of an application specific integrated circuit (xe2x80x9cASICxe2x80x9d). This type of conventional display apparatus is undesirable in that it is xe2x80x9cpin constrainedxe2x80x9d. In other words, an excessively large number of IC pins are required to drive a large-scale display apparatus.
Another factor of a conventional display device is that the current that is required from the ASIC for driving each visual indicator determines the drive strength of the pad cell. As the amount of current provided by the ASIC increases so does the drive strength of the pad cell. Therefore, more power, and hence power and ground pins on the ASIC are required to drive the display.
Still another factor of a conventional display device involves the brightness and process for illuminating various LED colors. When a conventional display apparatus having a red and a green colored LED needs to produce an amber color, both the red and green LED must be simultaneously illuminated. To do this, two pins of an ASIC must be activated simultaneously. Therefore, twice the power must be used to create an amber colored indicator. Similarly, when a display apparatus needs to illuminate a high threshold voltage LED or light colored LED, such as yellow, the standard power used for the low threshold voltage LED or dark colored LED, such as red, green, blue, etc., is not adequate. Therefore, a conventional display apparatus that needs to effectively illuminate a yellow LED must increase the power to the respective ASIC pin for the same.
In summary, each additional pin of an integrated circuit (xe2x80x9cICxe2x80x9d) or ASIC required to drive the visual indicators of a conventional display device eliminates other possible functions that the pins of the IC could be used for, or forces the use of larger and more expensive IC packages to drive the display device. In addition, conventional display devices can not display an amber color without simultaneously activating a red and a green LED, and can not effectively illuminate a high threshold voltage LED.
It is an object of the present invention to overcome some, if not all of the limitations of a convention display apparatus as described above.
In one embodiment of the invention an apparatus is provided for illuminating two dependent visual indicators with a single control line. The apparatus includes two visual indicators, two amplifiers, and a logic circuit. The same end of the two visual indicators connect to a conductive terminal. A first amplifier connects between the line and the other end of one indicator and a second amplifier connects between the line and the other end of the other indicator. A combination of signals applied to the two inputs selectively illuminates one or both indicators with one signal from the control line.
In another embodiment of the present invention, a process is disclosed for controlling the illumination of two dependent visual indicators with a single control line coupled to a logic circuit. The process includes simultaneously providing one of a HIGH and a LOW signal to a first and second input of the logic circuit to create one signal on the one control line. The signal on the control line illuminates the two indicators simultaneously, illuminates one of the two visual indicators or fails to illuminate either of the two indicators.